Looking at P40 Speed Performance Numbers...

[ElAurens]

And there are some very strange anomalies, be sure.

When looking at the numbers in "America's Hundred Thousand", they bring up more questions than ones they answer.

First off a bit of background, and I will concern myself only with Hawk 87 models here as that is what we will be getting in 4.12.

The early high production model, the E, is shown as the fastest Hawk 87 with a speed of 360 mph at 15000ft. at MILITARY (not COMBAT/WEP) power. It had a basic weight of 6702lbs. not including ammo and fuel. As newer models came down the line their weights went up and top speeds came down some, or in the case of the Merlin powered F the speed curve just went UP the altitude curve to just under 365mph at 20,000ft.

Seeing that the P40s were getting ever porkier Curtiss made an effort to lighten the last production model, the N, and they were successful, getting it's BASIC weight down to 6717lbs, from the portly M's 6899lbs. However, it's top speed is listed as some 15 to 20mph lower than the P 40E, at 345 ish mph. at a slightly higher altitude. Still at MILITARY, not COMBAT power.

Something is not adding up here, as other sources I recall show the Ns as the fastest production models.

I'll keep looking for answers, but anyone else have any clues?

[ElAurens]

Here are the engine types and ratings for various Hawk 87s...

P-40D, E and E-1: V-1710-39/F3R
T.O.: 1150bhp @ 3000rpm @ Sea Level. Manifold Pressure 46.2" HG.
Military: 1150bhp @ 3000rpm @ 12000ft.
Normal: 1000BHP @ 2600rpm @ 11000ft. Manifold Pressure 38.7" HG.

P40F: V-1650-1 Merlin
T.O.: 1300bhp @ 3000rpm @ Sea Level. Manifold Pressure 54.3" HG.
Military: 1240bhp @ 3000rpm @11800ft. Manifold Pressure 48.2" HG.
Normal: 1080bhp @ 2650rpm @ 9500ft. Manifold Pressure 44.2" HG.

P-40K: V-1710-73/F4R
T.O.: 1325 @ 3000rpm @ Sea Level No MP given.
War Emerg. : 1550bhp @ 3000rpm @ Sea Level(Rammed)
Military: 1150bhp @ 3000rpm @ 11800ft.
Normal: 1000 @ 2600rpm @ 11000ft.

P-40M/N-1: V-1710-81/F20R
P-40N20/-35: V-1710-99/F26R
P-40N-40: V-1710-115/F312R
T.O.: 1200 @ 3000rpm @ Sea Level
W.E.: 1360 @ 3000rpm @ Sea Level(Rammed)
Military: 1125 @ 3000rpm @ 14600~15500ft.
Normal: 1000 @ 2600rpm @ 13800~14000ft.

[secretone]

I am no expert and I ask the following question in the spirit of learning. Did the Merlin in the P-40F have a two stage compressor like in the Mustang and Spitfire? I understand that the Allisons did not... If so, then I do not see why it was not the fastest of the p-40 series.

[IceFire]

What does the "Rammed" indication mean at Sea Level?

Interesting that the K seems to have the greatest power? What's the story there?

[ElAurens]

I am no expert and I ask the following question in the spirit of learning. Did the Merlin in the P-40F have a two stage compressor like in the Mustang and Spitfire? I understand that the Allisons did not... If so, then I do not see why it was not the fastest of the p-40 series.

It was a two speed supercharger, not a two stage one, unlike the P 51, Spitfire, etc... that had 2 speed, 2 stage units. The F was the fastest above 15000ft.

[ElAurens]

What does the "Rammed" indication mean at Sea Level?

Interesting that the K seems to have the greatest power? What's the story there?


They are taking into account the effect of the air being rammed into the carb intake because of aircraft speed, unlike when an engine is running on the ground attached to a dynamometer.

[secretone]

So there was not a huge increase in performance in the F model because the blower was only single stage. Apparently Packard was not yet producing the 2 stage version of the motor at the time the F model was in production.

Here is a discussion thread for anyone who wants to explore this further:

http://www.ww2aircraft.net/forum/aviation/v-1650-powered-p-40s-30910.html

[ElAurens]

Interesting discussion there, thanks for the link.

[JG27_PapaFly]

Seeing that the P40s were getting ever porkier Curtiss made an effort to lighten the last production model, the N, and they were successful, getting it's BASIC weight down to 6717lbs, from the portly M's 6899lbs. However, it's top speed is listed as some 15 to 20mph lower than the P 40E, at 345 ish mph. at a slightly higher altitude. Still at MILITARY, not COMBAT power.

Something is not adding up here, as other sources I recall show the Ns as the fastest production models.

I'll keep looking for answers, but anyone else have any clues?

Depending on a plane's specific configuration, a decrease in wingload can increase drag in high-speed flight. Sailplanes get significantly improved lift-to-drag ratios and therefore higher cross-country speeds at high speeds by filling water into their wing tanks.

One other contributing aspect is that a change in wingloading often changes the relative positons of the center of gravity and center of lift. This influences the trim drag. CG position has to be optimized in order to minimize trim drag at high speeds. However, optimal CG placement for high-speed flight might be prohibitive due to stability/safety reasons.

[ElAurens]

Understood Papafly, but the N is still a bit heavier than the E which is faster than the N in the numbers I have ready at hand.

Odd.

[JG27_PapaFly]

Hmmm, maybe a difference in trim drag?

As long as we don't have reliable top speed figures we can only speculate...

[CadMan]

A few P-40 goodies

http://nzff.org/forum/index.php?showtopic=17913

[JtD]

I'd always recommend these pages:

http://www.raafwarbirds.org.au/targetvraaf/p40_archive/p40_data.htm
http://www.wwiiaircraftperformance.org/P-40/P-40.html